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Securities - Summary of Gross Unrealized Losses and Fair Values, Aggregated by Investment Category and Length of Individual Securities Continuous Unrealized Loss Position Available-for-sale (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Security	Dec. 31, 2016 USD ($) Security
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	101	88
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 39,896	$ 568,131
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	(407)	(12,893)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	455,688	14,719
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(12,010)	(297)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	495,584	582,850
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (12,417)	$ (13,190)
U.S. Treasury Notes
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	5	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 4,998	$ 9,918
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	(2)	(79)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	9,865
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(134)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	14,863	9,918
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (136)	$ (79)
U.S. Government Agencies
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	9	10
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 992	$ 58,857
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	(7)	(1,323)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	51,966
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(1,283)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	52,958	58,857
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (1,290)	$ (1,323)
Obligations of States, Municipalities, and Political Subdivisions
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	29	14
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 16,059	$ 7,799
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	(137)	(259)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	4,453	115
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(198)	(13)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	20,512	7,914
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (335)	$ (272)
Agency, Residential Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	41	41
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 15,441	$ 364,713
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	(181)	(8,483)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	292,016	3,447
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(7,465)	(157)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	307,457	368,160
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (7,646)	$ (8,640)
Non-Agency, Residential Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	1	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value		$ 19,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses		(174)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	$ 4,565
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(75)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	4,565	19,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (75)	$ (174)
Agency, Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	7	8
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value		$ 70,762
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses		(1,488)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	$ 57,442	6,641
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(1,966)	(63)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	57,442	77,403
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (1,966)	$ (1,551)
Non-Agency, Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	5	5
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value		$ 31,052
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses		(1,009)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	$ 30,971
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(792)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	30,971	31,052
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (792)	$ (1,009)
Corporate Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	3	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 2,406	$ 5,097
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	(80)	(78)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	2,489	2,522
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(24)	(8)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	4,895	7,619
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (104)	$ (86)
Other Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security	1	1
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	$ 1,921	$ 1,994
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(73)	(56)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	1,921	1,994
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses	$ (73)	$ (56)

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- Definition

Amount of unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Amount of unrealized loss on securities classified as available-for-sale.

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Amount of unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months.

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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